This invention relates to concepts relating to folding of paperboard sheets and other flexible sheet material, and more particularly to the folding of corrugated cardboard along a preformed score line in the manufacture of boxes and other containers in the art of packaging.
It is known to pass a sheet of paperboard or the like through a machine which causes the sheet to be folded. U.S. Pat. No. 4,614,512, for example, discloses a device wherein a scored sheet passes through and between folding elements consisting of a pair of fixed spiral bars which fold the sheet ends up and over through an arc of over 90.degree.. U.S. Pat. No. 4,624,653 discloses a device wherein a carton is erected, and in so doing, a corner flap is folded progressively between a longitudinal row of rollers and a spiral row of conical rollers which bend the flap. The rollers are fixedly mounted on suitable guides.
The known devices, such as those specifically mentioned above, cause a gradual bending and curving of the sheet between its leading and trailing edges, thus undesirably distorting it from its normal flat condition during folding. In addition, the folding apparatus confronts the leading edge of the sheet in such a way that the edge is forceably pushed by the apparatus in a direction contrary to the path the sheet would normally take; thus causing the edge to be subject to wear and damage.
Other known devices utilize folding mechanisms having protrusion carrying timing belts.
Other undesirable stress forces have also occured at the leading edge.
It is an object of the present invention to overcome the above-mentioned and other disadvantages inherent in the known devices. It is a further object to provide a new manner of handling and folding the sheets which effectively eliminates distortion of the traveling sheets as well as eliminating damaging contact with the leading edges thereof. It is yet another object to handle a plurality of sheets in an efficient, yet fast, manner from the beginning to the end of the folding cycle and through any desired arc.
In accordance with the various aspects of the invention, a plurality of longitudinally in-line sheet contactor members, called contactors, are provided, each of which are controllably movable so as to collectively pivot a sheet about its score line. The contactors are controlled so that they have a successive undulating wave action. Furthermore, the contactors are formed in sets including a sheet infeed set and a sheet discharge set, and in the present embodiment an intermediate set is disposed therebetween.
All of the contactors in the various sets are arranged to have a fixed preset or "at rest" position from which they move. Under the influence of a control device, the contactors individually and, in the present embodiment, pivotally move through varying angles from their respective at rest positions to contact and fold the sheet. The incremental angular displacement of each contactor is such that it becomes positioned at a point which corresponds with the at rest position of the next succeeding downstream contactor. Thus the leading edge of a sheet progressing from one contactor station to the next downstream station will not be subject to lateral distortion. Furthermore, the contactor and sheet positions are coordinated so that any group of contactors in contact with the sheet at any given time throughout the cycle are disposed in a straight line. The result is that the sheet is subjected only to straight line bending forces along the entire length of the portion to be folded, by the pivoting contactors, with essentially no stress and/or distortion created.
The sheet infeed set of contactors is such that each contactor has the same at rest position--normally horizontal or 0.degree.. The maximum angular displacement of each succeeding downstream infeed contactor, however, increases incrementally from the maximum angular displacement of the next preceding contactor. The timing is such that an entire sheet is accommodated by the infeed contactor set and about to enter the next downstream set before the infeed contactors begin to pivot. The pivoting begins simultaneously, with all of the infeed contactors initially pivoting together at the same angle, thus carrying the sheet portion to be folded in a straight line parallel to the score line.
In the present embodiment, the contactors of the next downstream or intermediate set have progressively increasing angular at rest positions, with the most upstream contactor therein having an at rest position corresponding or parallel to the input angle of the sheet as the leading edge of the sheet begins to leave the infeed set. This action continues progressively from contactor to contactor as the sheet moves progressively downstream in view of the fact that the maximum angular displacement of each succeeding intermediate set contactor also increases incrementally from the maximum angular displacement of the next preceding contactor. Contactors "dropping off" behind the trailing edge of the moving sheet return to their at rest positions. At any given moment, all of the group of contactors which are contacting the sheet are at the same angular position. Thus, the sheet portion being folded continues to be pivoted in a straight line contact by the contactors and about the score line.
The sheet discharge set of contactors also have progressively increasing angular at rest positions, with the most upstream contactor therein having an at rest position corresponding or parallel to the input angle of the sheet as the leading edge of the sheet begins to leave the nextmost upstream or intermediate set. As with the intermediate set, this action continues progressively downstream with all of the group of contactors which are contacting the sheet being at the same angular position. However, the last number of contactors corresponding to the number of contactors in the infeed set and corresponding to the length of a full sheet have a constant usable maximum angle, to accommodate the sheet in a straight line as the sheet reaches its maximum angular position, such as 90.degree. and actually up to 180.degree..
The change in contactor angle from the at rest to the maximum position, for the full cycle, is thus: Increasing angle change in the infeed set, constant angle change in the intermediate set, and finally decreasing angle change in the discharge set which corresponds in reverse to the infeed set.
In the present embodiment, the contactors constitute free wheeling rollers which are mounted on brackets and with the rollers having axes defining the various at rest and other angular positions. The brackets are connected to lever arms which in turn are pivotable about an axis closely adjacent and parallel to the score line in the sheets. The device for positioning and moving the rollers includes a rotatable shaft carrying a plurality of cams which define the various "at rest" and angular positions of the rollers. The shaft and cam positions are coordinated with the sheet positions by a suitable control.